Ultrasound array transmitter architecture with high timing resolution using embedded phase-locked loops

Coarse time quantization of delay profiles within ultrasound array systems can produce undesirable sidelobes in the radiated beam profile. The severity of these sidelobes is dependent upon the magnitude of phase quantization error - the deviation from ideal delay profiles to the achievable quantized case. This paper describes a method to improve inter channel delay accuracy without increasing system clock frequency by utilising embedded Phase-Locked Loop (PLL) components within commercial Field Programmable Gate Arrays (FPGAs). Precise delays are achieved by shifting the relative phases of embedded PLL output clocks in 208 ps steps. The described architecture can achieve the necessary inter element timing resolution required for driving ultrasound arrays up to 50 MHz. The applicability of the proposed method at higher frequencies is demonstrated by means of extrapolating experimental results obtained using a 5 MHz array transducer. Results indicate an increase in Transmit Dynamic Range (TDR) when using accurate delay profiles generated by the embedded PLL method described, as opposed to using delay profiles quantized to the system clock

A Computational Model for Continuous Cooling of Injection Moulding Processes

This paper discusses the approaches and techniques used to build a realistic numerical model to analyse the cooling phase of the injection moulding process. The procedures employed to select an appropriate mesh and the boundary and initial conditions for the problem are discussed and justified. The final model is validated using direct comparisons with experimental results generated in an earlier study. The model is shown to be a useful tool for further studies aimed at optimising the cooling phase of the injection moulding process. Using the numerical model provides additional information relating to changes in conditions throughout the process, which otherwise could not be deduced or assessed experimentally. These results, and other benefits related to the use of the model, are also discussed in the paper

Luminosities of AGB Variables

The prevailing evidence suggests that most large-amplitude AGB variables follow the period luminosity (PL) relation that has been established for Miras in the LMC and galactic globular clusters. Hipparcos observations indicate that most Miras in the solar neighbourhood are consistent with such a relation. There are two groups of stars with luminosities that are apparently greater than the PL relation would predict: (1) in the LMC and SMC there are large amplitude variables, with long periods, P> 420 days, which are probably undergoing hot bottom burning, but which are very clearly more luminous than the PL relation (these are visually bright and are likely to be among the first stars discovered in more distant intermediate age populations); (2) in the solar neighbourhood there are short period, P<235 days, red stars which are probably more luminous than the PL relation. Similar short-period red stars, with high luminosities, have not been identified in the Magellanic Clouds.Comment: 8 pages, 2 figure, to be published in Mass-Losing Pulsating Stars and their Circumstellar Matter, Y. Nakada & M. Honma (eds) Kluwer ASSL serie

Component test facilities for marine renewable energy converters

This paper describes how the PRIMaRE group at University Exeter is engaging in the establishment of appropriate reliability methods suitable for application to marine renewable devices with a key area being the production of suitable failure rate data for the marine renewable energy industry. This activity seeks to mitigate uncertainties and cost implications associated with the reliability assessment of marine energy converters (MECs) due to an omnipresent lack of applicable failure rate data. The capability of two facilities, namely i) the South Western Mooring Test Facility (SWMTF) and ii) the Dynamic Marine Component Test facility (DMaC), to perform specimen and accelerated component testing is discussed. A case study, using data from wave tank tests and numerical simulations performed for the SWMTF, serves to illustrate how evidence of component reliability under operational conditions could be provided.The authors would like to acknowledge the support of the South West Regional Development Agency through the PRIMaRE institution. They would also like to acknowledge the European Community's Sixth Framework Programme HYDRALAB III, Contract no. 022441 (RII3). The second author would like to acknowledge the funding support from the Engineering and Physical Sciences Research Council (EPSRC) under the SUPERGEN Marine Doctoral Programme. Thanks also to Orcina for provision of their Orcaflex software

Confirmatory factor analysis of the Test of Performance Strategies (TOPS) among adolescent athletes

The aim of the present study was to examine the factorial validity of the Test of Performance Strategies (TOPS; Thomas et al., 1999) among adolescent athletes using confirmatory factor analysis. The TOPS was designed to assess eight psychological strategies used in competition (i.e. activation, automaticity, emotional control, goal-setting, imagery, negative thinking, relaxation and self-talk,) and eight used in practice (the same strategies except negative thinking is replaced by attentional control). National-level athletes (n = 584) completed the 64-item TOPS during training camps. Fit indices provided partial support for the overall measurement model for the competition items (robust comparative fit index = 0.92, Tucker-Lewis index = 0.88, root mean square error of approximation = 0.05) but minimal support for the training items (robust comparative fit index = 0.86, Tucker-Lewis index = 0.81, root mean square error of approximation = 0.06). For the competition items, the automaticity, goal-setting, relaxation and self-talk scales showed good fit, whereas the activation, emotional control, imagery and negative thinking scales did not. For the practice items, the attentional control, emotional control, goal-setting, imagery and self-talk scales showed good fit, whereas the activation, automaticity and relaxation scales did not. Overall, it appears that the factorial validity of the TOPS for use with adolescents is questionable at present and further development is required

Morphological effects of porous poly-D,L-lactic acid/hydroxyapatite scaffolds produced by supercritical CO2 foaming on their mechanical performance

A novel supercritical CO2 foaming technique was used to fabricate scaffolds of controllable morphology and mechanical properties, with the potential to tailor the scaffolds to specific tissue engineering applications. Biodegradable scaffolds are widely used as temporary supportive structures for bone regeneration. The scaffolds must provide a sufficient mechanical support while allowing cell attachment and growth as well as metabolic activities. In this study, supercritical CO2 foaming was used to prepare fully interconnected porous scaffolds of poly-D,L-lactic acid and poly-D,L-lactic acid/hydroxyapatite. The morphological, mechanical and cell behaviours of the scaffolds were measured to examine the effect of hydroxyapatite on these properties. These scaffolds showed an average porosity in the range of 86%–95%, an average pore diameter of 229–347 µm and an average pore interconnection of 103–207 µm. The measured porosity, pore diameter, and interconnection size are suitable for cancellous bone regeneration. Compressive strength and modulus of up to 36.03 ± 5.90 and 37.97 ± 6.84 MPa were measured for the produced porous scaffolds of various compositions. The mechanical properties presented an improvement with the addition of hydroxyapatite to the structure. The relationship between morphological and mechanical properties was investigated. The matrices with different compositions were seeded with bone cells, and all the matrices showed a high cell viability and biocompatibility. The number of cells attached on the matrices slightly increased with the addition of hydroxyapatite indicating that hydroxyapatite improves the biocompatibility and proliferation of the scaffolds. The produced poly-D,L-lactic acid/hydroxyapatite scaffolds in this study showed a potential to be used as bone graft substitutes

HLA-DR genotyping and mitochondrial DNA analysis reveal the presence of family burials in a fourth century Romano-British Christian cemetery

In Colchester, Britain's oldest recorded town, during the Roman period there were areas which were clearly used solely as cemeteries. One o f the most significant is at Butt Road, which includes a late Roman probable Christian cemetery with an associated building, apparently a church, that overlies and developed from a pagan inhumation cemetery. DNA was extracted from the long bones (femurs) of 29 individuals, mostly from a large complex of burials centered on two timber vaults. These were thought to comprise a number of family groupings, deduced from osteological analysis, stratigraphical and other considerations. The use of a modified version of the silica-based purification method recovered nanogram quantities of DNA/gram of bone. Two-stage amplification, incorporating primer-extension preamplification-polymerase chain reaction, permitted simultaneous amplification of both mitochondrial and nuclear DNA. Sequence-specific oligonucleotide probes yielded human leukocyte antigen (HLA)-DR typing of seven samples, with four revealing the infrequent HLA-DR10 genotype. Examination of the control region of mitochondrial DNA (mtDNA) by direct sequencing revealed polymorphisms yet to be reported in the modern population. HLA-DRB typing and mtDNA analysis affirmatively supported kinship among some, if not all, individuals in the "vault complex" and demonstrate a continental European origin of the individuals investigated

Utilization of a deoxynucleoside diphosphate substrate by HIV reverse transcriptase

Background: Deoxynucleoside triphosphates (dNTPs) are the normal substrates for DNA sysnthesis is catalyzed by polymerases such as HIV-1 reverse transcriptase (RT). However, substantial amounts of deoxynucleoside diphosphates (dNDPs) are also present in the cell. Use of dNDPs in HIV-1 DNA sysnthesis could have significant implications for the efficacy of nucleoside RT inhibitors such as AZT which are first line therapeutics fro treatment of HIV infection. Our earlier work on HIV-1 reverse transcriptase (RT) suggested that the interaction between the γ phosphate of the incoming dNTP and RT residue K65 in the active site is not essential for dNTP insertion, implying that this polymerase may be able to insert dNPs in addition to dNTPs. Methodology/Principal Findings: We examined the ability of recombinant wild type (wt) and mutant RTs with substitutions at residue K65 to utilize a dNDP substrate in primer extension reactions. We found that wild type HIV-1 RT indeed catalyzes incorporation of dNDP substrates whereas RT with mutations of residue K645 were unable to catalyze this reaction. Wild type HIV-1 RT also catalyzed the reverse reaction, inorganic phosphate-dependent phosphorolysis. Nucleotide-mediated phosphorolytic removal of chain-terminating 3′-terminal nucleoside inhibitors such as AZT forms the basis of HIV-1 resistance to such drugs, and this removal is enhanced by thymidine analog mutations (TAMs). We found that both wt and TAM-containing RTs were able to catalyze Pi-mediated phosphorolysis of 3′-terminal AZT at physiological levels of Pi with an efficacy similar to that for ATP-dependent AZT-excision. Conclusion: We have identified two new catalytic function of HIV-1 RT, the use of dNDPs as substrates for DNA synthesis, and the use of Pi as substrate for phosphorolytic removal of primer 3′-terminal nucleotides. The ability to insert dNDPs has been documented for only one other DNA polymerase The RB69 DNA polymerase and the reverse reaction employing inorganic phosphate has not been documented for any DNA polymerase. Importantly, our results show that Pi-mediated phosphorolysis can contribute to AZT resistance and indicates that factors that influence HIV resistance to AZT are more complex than previously appreciated. © 2008 Garforth et al

Exploring the equity of GP practice prescribing rates for selected coronary heart disease drugs: a multiple regression analysis with proxies of healthcare need

Background There is a small, but growing body of literature highlighting inequities in GP practice prescribing rates for many drug therapies. The aim of this paper is to further explore the equity of prescribing for five major CHD drug groups and to explain the amount of variation in GP practice prescribing rates that can be explained by a range of healthcare needs indicators (HCNIs). Methods The study involved a cross-sectional secondary analysis in four primary care trusts (PCTs 1–4) in the North West of England, including 132 GP practices. Prescribing rates (average daily quantities per registered patient aged over 35 years) and HCNIs were developed for all GP practices. Analysis was undertaken using multiple linear regression. Results Between 22–25% of the variation in prescribing rates for statins, beta-blockers and bendrofluazide was explained in the multiple regression models. Slightly more variation was explained for ACE inhibitors (31.6%) and considerably more for aspirin (51.2%). Prescribing rates were positively associated with CHD hospital diagnoses and procedures for all drug groups other than ACE inhibitors. The proportion of patients aged 55–74 years was positively related to all prescribing rates other than aspirin, where they were positively related to the proportion of patients aged >75 years. However, prescribing rates for statins and ACE inhibitors were negatively associated with the proportion of patients aged >75 years in addition to the proportion of patients from minority ethnic groups. Prescribing rates for aspirin, bendrofluazide and all CHD drugs combined were negatively associated with deprivation. Conclusion Although around 25–50% of the variation in prescribing rates was explained by HCNIs, this varied markedly between PCTs and drug groups. Prescribing rates were generally characterised by both positive and negative associations with HCNIs, suggesting possible inequities in prescribing rates on the basis of ethnicity, deprivation and the proportion of patients aged over 75 years (for statins and ACE inhibitors, but not for aspirin)

Candida albicans repetitive elements display epigenetic diversity and plasticity

Transcriptionally silent heterochromatin is associated with repetitive DNA. It is poorly understood whether and how heterochromatin differs between different organisms and whether its structure can be remodelled in response to environmental signals. Here, we address this question by analysing the chromatin state associated with DNA repeats in the human fungal pathogen Candida albicans. Our analyses indicate that, contrary to model systems, each type of repetitive element is assembled into a distinct chromatin state. Classical Sir2-dependent hypoacetylated and hypomethylated chromatin is associated with the rDNA locus while telomeric regions are assembled into a weak heterochromatin that is only mildly hypoacetylated and hypomethylated. Major Repeat Sequences, a class of tandem repeats, are assembled into an intermediate chromatin state bearing features of both euchromatin and heterochromatin. Marker gene silencing assays and genome-wide RNA sequencing reveals that C. albicans heterochromatin represses expression of repeat-associated coding and non-coding RNAs. We find that telomeric heterochromatin is dynamic and remodelled upon an environmental change. Weak heterochromatin is associated with telomeres at 30?°C, while robust heterochromatin is assembled over these regions at 39?°C, a temperature mimicking moderate fever in the host. Thus in C. albicans, differential chromatin states controls gene expression and epigenetic plasticity is linked to adaptation